1. Field of the Invention
This invention relates generally to monitoring and data acquisition devices and, more particularly to a low-power triggered data acquisition system and method utilizing low-powered circuitry and digital logic incorporated into a miniaturized device interfaced with self-generating transducer sensor inputs to detect, identify and assess impact and damage to surfaces and structures wherein, upon the occurrence of a triggering event that produces a signal greater than a set threshold causes the system to acquire and store digital data representative of an incoming waveform on at least one triggered channel.
2. Background Art
Prosser, et al, U.S. Pat. No. 6,628,567 discloses an acoustic monitoring device having at least two acoustic sensors with a triggering mechanism and a multiplexing circuit. After the occurrence of a triggering event at a sensor, the multiplexing circuit allows a recording component to record acoustic emissions at adjacent sensors. The acoustic monitoring device is attached to a solid medium to detect the occurrence of damage.
Devices for acquiring high-speed transient signals, for example acoustic emissions, typically require data acquisition electronics that are in a high-power mode for acquiring data on at least one channel at the full data acquisition rate. The power consumption of these high-speed data acquisition electronics is significantly high. To determine if the acquired data is a transitory event of interest, a digital circuit must process the acquired digital data in some way, which requires a significant amount of power and processor resources. Acquired data must be stored in digital memory temporarily while the data is processed, such that if a transient event of interest is detected, the acquired data can be obtained. Continuously storing data to memory requires a significant amount of power.
Continuous damage detection and characterization for various structures has been an elusive goal due to the transitory nature of the detectable high-frequency signals. A variety of techniques for detecting damage exist for using piezoelectric transducers to detect damage on aircraft, manned spacecraft, ships and underwater vehicles, motorized vehicles, storage tanks, pressure vessels, and civil structures. These techniques generally require the use of large numbers of piezoelectric sensor channels to be distributed throughout the structure to be monitored. Further, these sensors must be monitored continuously for transient signals that are indicative of damage, such as cracking, delamination, and impact. However, the size, complexity, and power consumption of the necessary electronics to acquire, process, and store the resulting digital waveforms is often too large to be included in operational vehicles or structures.
Various techniques have been used to monitor vehicles and structures for impact with micrometeoroids and orbital debris (MMOD) or other shock events in the past. Many involve the high-speed data acquisition and processing of large numbers of individual sensors, which are all wired back to a central location. Although capable of detecting events, the vehicle resources required for the systems, such as power, mass, and volume, have been excessive.
Invocon, Inc., of Conroe, Tex., also the owner of the present invention, has provided a wireless impact detection system to NASA for integration on the shuttle wing leading edges for the return to flight mission, and subsequent missions. The system records data from three channels of accelerometers at 20 k samples per second, performs post-processing algorithms to identify regions of raw launch data that may indicate an impact event, and then transmits only the processed data via RF through a wireless network to a laptop in the crew compartment. Although this system meets the requirements for monitoring the wing leading edges during launch, its ability to monitor throughout the entire mission for MMOD impacts is severely limited by battery power. Despite using the lowest power data acquisition and DSP electronics available, each unit's dual AA-cell battery pack can support only up to 10 hours of data acquisition and processing. The present system is a significant improvement over the earlier system.